1. Field of the Invention
The present invention relates to a poly(lactide) copolymer and a process for manufacturing same.
2. Description of the Prior Art
The continued depletion of available landfill and other disposal sites have lead to an increasing need for improved waste management practices, including the replacement of non-biodegradable or partially biodegradable polymers with polymer resins which are biodegradable. Used in conjunction with improved waste management practices such as composting or recycling, biodegradable resins can help alleviate the environmental stress due to disposal of items such as packaging materials, coated paper products, films, single use diapers and the like.
Poly(lactide)s are biodegradable polymer resins derived from annually renewable resources. They have been used as specialty chemicals in the medical industry, but high costs and processing difficulties have prevented their widespread use to replace conventional polymers derived from petrochemicals. Recent processing developments, such as those disclosed by Gruber et al. (U.S. Pat. No. 5,142,023), the disclosure of which is incorporated herein by reference, have made it possible to provide lower cost poly(lactide) polymers for use in packaging and other high-volume, low-margin applications.
There are a number of technical problems which have heretofore stood in the way of developing a commercially viable poly(lactide) based replacement resin for existing conventional resins. Poly(lactide) is subject to unwanted degradation during melt processing via a number of pathways, including hydrolysis, and other side reactions which, for example, result in lactide formation. It would be desirable, therefore, to produce a melt-stable poly(lactide).
Furthermore, at high processing temperatures, polymer degradation is accelerated. Accordingly, even if a melt-stable poly(lactide) can be produced, it would be desirable to provide a poly(lactide) formulation which can be processed into useful articles at reduced temperatures.
In a typical coating application or in cast film production there is a tendency for neck-in as the polymer resin leaves the die, resulting in a film or coating with a thickening at the edge. This material must be trimmed to produce a uniform coating or film. These trimmings can often be recycled, but this exposes the polymer to more thermal stress and can lead to increased degradation. Accordingly, there is a need to provide a poly(lactide) formulation which will have reduced neck-in.
In a coating application or blown film production the polymer melt must withstand certain forces, such as acceleration in going from the die to the substrate in a coating application or the gas pressure which causes stretching in a blown film. The ability to withstand these forces is called "melt-strength". Accordingly, there is a need for a poly(lactide) formulation which will have improved melt-strength.
It is also worth noting that to gain widespread acceptance in the marketplace, films from which articles are made must have the sound and feel to which consumers have grown accustomed. Therefore, there is a need to provide a poly(lactide) formulation which will provide a film or article which will provide a better "feel" to the consumer and less noise when the film is crumpled.